1. Field of the Invention
The present invention relates generally to decomposition of waste materials, and more particularly but not by way of limitation, to a method and apparatus for thermally decomposing hazardous waste materials.
2. Description of the Prior Art
A problem of major concern for today's society is the disposal of waste material, especially a group of substances which have been designated by both federal and state authorities as "hazardous waste material". Hazardous waste materials are generally chemical substances which consist of product mixtures, such as polychlorinated biphenols (PCB's), pentachlor phenols, organophosphorus, organonitrogen and organometallic compounds, as well as other materials that exist in large quantities and demand effective disposal procedures.
Of major concern in the disposal of hazardous waste materials is the fact that such materials are not only toxic, but such materials are in a composite matrix format often containing organic and inorganic components. Thus, the waste materials are generally thermally stable and not easily decomposed. Even when such compounds decompose, the result is that gases generated are often at least as toxic, if not more so, than the original waste material unless the decomposition process is highly controlled. Thus, the compounds themselves and any waste derived from the decomposition of such compounds may migrate into the ecological system in an uncontrolled manner when subjected to inferior decomposition processes.
The prior art is replete with various types of processes and apparatus for the decomposition of waste materials. Many of such processes employ combustion or incineration technology using various types of furnaces, incinerators or rotary kilns. More recently, plasma pyrolysis technology has been suggested as an effective method for the pyrolytic destruction of toxic waste materials.
Barton et al., U.S. Pat. No. 4,644,877, disclose the pyrolytic destruction of toxic or hazardous waste material using plasma torch technology wherein the waste materials are fed into a plasma arc burner for atomization and ionization prior to discharge into a reaction chamber to be cooled and recombined into product gas and particulate matter. The recombined products obtained from the cooling of the atomized and ionized waste material are quenched using a spray ring. An alkali atomized spray produced by the ring neutralizes the recombined products and wets the particulate matter. The product gas can then be extracted from the recombined products using a scrubber so that the product gas can be burned or used for fuel. Monitoring devices are employed in the apparatus to monitor the recombined products and to automatically shut down the apparatus if hazardous constituents are detected in the reaction chamber.
Faldt et al., U.S. Pat. No. 4,479,433 is also representative of the prior art relating to the thermal destruction of toxic or hazardous waste material using plasma torch technology.
Other methods for the disposal of hazardous waste materials, especially chemical substances such as polychlorinated biphenols (PCB's) have been proposed using the molten metal salt bath technology in which a molten metal salt bath is utilized in the decomposition of the waste materials. When employing the molten salt bath technology for the destruction of waste materials, the chemical substance sought to be destroyed and a source of oxygen are fed into a reactor containing the molten salt mixture which is maintained at a temperature of about 850.degree. C. The chemical component is purportedly decomposed by pyrolysis and oxidation upon contact with the molten salt mixture. However, several inherent problems exist when employing the molten salt technology for the thermal destruction of hazardous waste materials, namely: (a) the molten salt mixture is depleted during the decomposition of chemical compounds and has to be replaced, and (b) solid waste products formed from the decomposition of the waste materials often create additional disposal problems.
Thus, while numerous methods and apparatus have heretofore been proposed by the prior art for the destruction of hazardous waste materials, and while much progress has been made in the disposal of such materials especially through advancements in the plasma torch technology, a need remains for improved methods and apparatus for decomposing hazardous waste materials which are effective and do not suffer from the disadvantages of the methods and apparatus of the prior art. It is to such a method and apparatus that the present invention is directed.